Patent GB-1495149-A (GB)
Title: Switch-condition-transmitting device
IPC: B60C23/04
Filed: 1974-11-06
Abstract: 1495149 Switch condition transmitting arrangement JAEGER 6 Nov 1974 [7 Nov 1973 28 June 1974] 31578/77 Divided out of 1495148 Heading H4L [Also in Division B7] In an arrangement for transmitting the condition of a switch 3 (which may be fitted in a tyre pressure sensing arrangement such that loss of pressure opens the switch) the switch when closed serially connects at least two coils 2 in a first assembly 1, which is in combination with a second relatively movable assembly 4 incorporating a transmission coil 5 energized by generator 7 and a detection coil 6 such that in one relative position of the assemblies, the transmission coil 5 and detection coil 6 are inductively coupled with respective coils 2. A detecting arrangement incorporating a phase comparator 9 having inputs coupled to the generator 7 and detection coil 6 produces different outputs depending on whether the detection coil is excited only by the field of the transmission coil 5 (switch 3 open) or whether it is excited from the respective coil 2 of the first assembly (switch 3 closed). The phase comparator 9 is adjusted to provide no output in the open switch condition. A square wave output is obtained in the closed switch condition. This can be compared with the output from a similar arrangement V 2  (testing, e.g. another tyre), by passing both outputs to a memory circuit 11 in such a way that if both are the same, they cancel; if they are not the same, a warning at indicator 13 is given. Circuit details.-The transmitter circuit 7 incorporates an astable multivibrator (14, 15, Fig. 3, not shown) whose output is coupled to amplifier stages (15, 17) and thence to the transmitter coil. The receiving circuit (Fig. 4) incorporates cascaded amplifier stages 19, 20 followed by a separator stage 23, 26, 27. The transistor 21 is normally saturated; but is cut off, so letting the amplifier function, for a period following the leading edge of the transmitted pulse, which is applied to the transistor 22. When the mobile assembly is not near the coil 6, the signal which reaches transistor 23 prevents the charging of capacitor 24 in the period during which transistor 21 is cut off. When the mobile assembly is present, transistor 23 is cut off, C24 charges, transistor 26 saturates and transistor 27 cuts off, so that a logical "1" appears at "S", showing a closed switch and normal pressure in the tyre. In the storage and indicating circuit (Fig. 8, not shown) the pulse output from the transistor 27 is applied via a capacitor (60) and a diode (61) to a capacitor (28). The pulse output from a second receiving circuit is applied to a transistor (29R) in parallel with the capacitor, such that if both receiving circuits are providing pulse outputs, the capacitor alternately charges and discharges. If however the second circuit no longer provides signals to discharge the capacitor, its potential increases to activate a differential amplifier in the circuit 12 which controls the alarm device 13. Pulses from the first receiving circuit also control a transistor (29) across the storage capacitor (28R) in the circuit for the second receiving circuit, the output from which is applied to the control circuit 14. A switch (30) may be operated, e.g. by reverse gear of the vehicle to prevent alarm signals being given during reversing.